relationships:

watch can only work if it has enough
energy; only a finite amount of energy can be
stored

b) Adding domain knowledge

How users use the device: Fob watches are mainly used for
telling the time of day, of course. They are also used to work out
elapsed time (how long has this process been going on?),
time-remaining (how much longer will it go on?), time-of-completion
(what will the time be when this process has continued for X
minutes?), and current time in other time zones.

Domain concepts and relationships: From the above, three
domain concepts need to be introduced, time-elapsed, time-remaining,
and time-of-completion.

Context of usage, and related tools or devices: Because the
fob watch has no alarm system, it is frequently used in conjunction
with separate devices for countdown timing (e.g. egg-timers) and for
reminders at set times (e.g. alarm clocks). Transferring data from
one of these to another may require translation between digital and
analogue time representations.

c) Expanding the device description

conceptual
action

device
actions

device object

persistence

disguised?

notes

turn knob (when out)

pull knob out, turn it, press it
back in

knob

high

no

moded: knob must be out to change
time

wind knob

turn knob

knob

high

no

moded

find elapsed time

read current time and subtract a
previous time (possibly recorded on a sub-device such as
paper; possibly from memory)